The present invention relates to a wind power plant having a rotor being rotatably mounted with respect to a rotor axis by means of a bearing arrangement and having at least one rotor blade attached to a rotor hub and extending therefrom radially in an outward direction with respect to the rotor axis, as well as a bearing arrangement for such a wind power plant.
Typically, wind power plants of the above described type have a tower with a rotor being mounted at the top of said tower and being rotatably run on bearings about a rotation axis extending substantially in a horizontal direction. For adjusting the wind power plant to the wind conditions, usually the rotor together with the bearing arrangement can be rotated about a rotation axis extending in a pivoting direction. To this end, the bearing arrangement, the rotor, a gear coupled to the rotor (if provided), and a generator coupled to the gear at the output end are disposed on a platform rotatably mounted on the top of the tower. In modern wind power plants having a nominal power of several megawatts, the rotor may have a diameter of more than 100 m. In these wind power plants, the torque is typically applied to the generator by means of a rotor shaft screwed to the rotor hub via a flange. The rotor shaft intersperses a bearing block disposed on the platform which is rotatable about the vertical rotation axis, and its end opposite to the rotor hub is counterbeared via a clamping set to the input of a gear, the output of said gear being coupled to the generator.
During long-term operation of wind power plants of the above described type is turned out that crack initiation occurred in the rotor shafts typically being formed as hollow shafts, so that replacement of the rotor shaft is necessitated to prevent breakage thereof and, as a consequence thereof, the risk of a rotor crash.
In view of these problems associated with the prior art, it is an object of the present invention to provide a wind power plant of the previously described type which allows for low-maintenance long-term operation as well as to provide a bearing arrangement for such a wind power plant.
According to the present invention, this object is solved by an improved wind power plant of the previously described type which is essentially characterized in that the bearing arrangement comprises a first bearing ring being fixed to a support arrangement in a torque proof manner, with respect to the rotor axis, and being disposed coaxially with the rotor axis, as well as a second bearing ring being also disposed coaxially with the rotor axis but being supported on the first bearing ring in a rotatable manner, with respect to the rotor axis, and being fixed to the rotor hub.
This invention is based on the insight that the deficiencies observed during operation of the known wind power plants are primarily due to the fact that not only torque is transferred by the rotor shaft but also every other load like, e.g., the weight of the rotor comprised of the rotor hub and the rotor blades, and operational shearing or tilting moments are applied thereto. In contrast to this, in the wind power plant according to the present invention, the gravitational forces and operational shearing or tilting moments are transferred by the first bearing ring whereas the second bearing ring and a torque transmission arrangement being attached thereto where required, have only to bear the torque. Thus, damage due to loads of the second bearing ring and/or a torque transmission arrangement being coupled thereto where required, can be avoided even during long-term operation of the wind power plant.
Even though also the use of gearless wind power plants with synchronous generators where the second bearing ring is directly coupled to the generator, is within the scope of the present invention, is turned out to be especially beneficial for an increase in efficiency that the rotor is coupled to the input of a gear box which can be coupled to a generator at its output side.
Especially, in the previously described embodiment of the present invention it proved to be favorable with respect to the above-mentioned load distribution that the wind power plant according to the present invention has a torque transmission arrangement extending, when starting from the second bearing ring preferably directly mounted to the rotor hub, radially inwardly with respect to the rotor axis.
In modern wind power plants, the rotor blades are mounted to the rotor hub so that they can rotate about their longitudinal axis for adjustment to the actual wind conditions. To this end, normally pitch drives are provided in the rotor hub which is in general formed as a casting. The pitch drives can cause the rotor blades to rotate about their longitudinal axis. Additionally or alternatively, aerodynamical tools can be provided like, e.g., adjustable rotor blade tips and/or rotor blade flaps which can be adjusted by drives accommodated in the rotor hub. To this end, the rotor hub is normally formed as a hollow body.
For facilitating of maintenance of such wind power plants, it proved to be especially favorable if the torque transmission arrangement extending, when starting from the second bearing ring preferably directly mounted to the rotor hub, radially inwardly with respect to the rotor axis has at least one passage opening allowing for access to the interior of the rotor hub because, thus, the drives accommodated in the hub are accessible from the platform or a nacelle formed thereon in an especially easy way. Thereby, access may occur independently from a respective position of the rotor. Further facilitation of access to the elements of the wind power plat which are accommodated in the rotor hub is achieved if the torque transmission arrangement has a spoke wheel with two, three or more passage openings and fixed to the second bearing ring.
As a result, access to the rotor hub is provided independent of atmospheric influence.
From a design aspect, the bearing arrangement of a wind power plant according to the present invention can be realized especially simple by a roller bearing, the outer ring (inner ring) thereof being formed by the first bearing ring and the inner ring (outer ring) thereof being formed by said second bearing ring.
As mentioned before, in a wind power plant according to the present invention the first bearing ring, which is fixed to the support arrangement in a torque-proof manner, bears the gravitational forces as well as operational shearing and tilting moments. Thereby, damage due to the forces applied to the support arrangement can be reliably prevented by a support arrangement having a sandwich structure with an inner support layer and an outer support layer, inner and outer being defined with respect to the rotor axis, and a filling layer disposed between said support layers. Thus, an especially high stiffness of the support arrangement is achieved, wherein the occurring shear forces can be absorbed by the filling layer disposed between the support layers.
For reducing the weight of the support arrangement, it proved appropriate that at least one of said support layers is formed as a tubular construction. The filling layer may comprise spacer for ensuring the spacing between the support layers, a honeycomb structure, polyurethane foam, metallic foam and/or a balsa core. Further to providing high stiffness and reduced weight, the support arrangement according to the present invention also provides noise insulation and excellent vibration damping. The transmission of force into the support arrangement can be accomplished via a bending resistant front flange of the support arrangement which is fixed to the first bearing ring.
As has been explained above, at least one rotor blade of the wind power plant according to the present invention may be fixed to the rotor hub so that it can be rotated about its longitudinal axis to thereby improve the efficiency of the wind power plant for varying wind conditions.
Although a complete housing of the single components of a wind power plant according to the present invention is not longer necessary when the support arrangement is formed as a tubular construction, it turned out to be of advantage in view of further efficiency improvement that at least the rotor hub is surrounded by a covering element at least in part.